On 03/07, Hillf Danton wrote: > > On Thu, 6 Mar 2025 10:30:21 +0100 Oleg Nesterov <oleg@xxxxxxxxxx> > > > > > > > > Yes, but in this case pipe_full() == true is correct, this writer can > > > > safely sleep. > > > > > > > No, because no reader is woken up before sleep to make pipe not full. > > > > Why the reader should be woken before this writer sleeps? Why the reader > > should be woken at all in this case (when pipe is full again) ? > > > "to make pipe not full" failed to prevent you asking questions like this one. Hmm. I don't understand your "prevent you asking questions" reply. If the pipe was full we do not need to wake the reader(s), the reader can only sleep if pipe_empty() == true. > > We certainly can't understand each other. Yes. > step-00 > pipe->head = 36 > pipe->tail = 36 > after 3d252160b818 > > step-01 > task-118762 writer > pipe->head++; > wakes up task-118740 and task-118768 > > step-02 > task-118768 writer > makes pipe full; > sleeps without waking up any reader as > pipe was not empty after step-01 > > step-03 > task-118766 new reader > makes pipe empty > sleeps but since the pipe was full, this reader should wake up the writer task-118768 once it updates the tail the 1st time during the read. > step-04 > task-118740 reader > sleeps as pipe is empty this is fine. > [ Tasks 118740 and 118768 can then indefinitely wait on each other. ] 118768 should be woken at step 3 ? Oleg.
